How Genetics Are Changing Grapevines

Researchers use genomics and genetic tools to fight pests and diseases

by Paul Franson
Grapevines growing along the Napa River in Yountville, Calif., have 94% Vitis vinifera parentage and are resistant to Pierce’s disease.
Napa, Calif.—Sometimes it seems as if a new pest or disease threatens California grapevines every week, but many tools are available to fight them. Three experts discussed some of the most promising approaches for fighting vineyard pests at the Napa Valley Grapegrowers’ Rootstock conference held Nov. 12

The title of the panel discussion was “The Future of Genomics and Genetic Tools for Grapevines,” and it featured Carole Meredith, professor emerita at the University of California, Davis, and co-owner of Lagier Meredith Vineyard on Mount Veeder in Napa County; Andy Walker, professor at UC Davis, and Marc Fuchs, associate professor at Cornell University.

The session was moderated by winemaker Aaron Pott, who discussed the popular fear of changes like genetic engineering but pointed out how improved grapevines could offer the possibility of eliminating the use of pesticides, reducing irrigation and overcoming climate changes.

Of course, a fundamental question is, “Why change grapevines?” They are well established, and some have proven very popular.

Researchers want to improve grape vines for a number of reasons including solving a problem like susceptibility to pests or diseases, and to overcome environmental limitations like climate, water shortages and degradation by salts in the soil.

Researchers also can seek to improve grape quality, increase yield or meet market demand.

Meredith started the discussion with an overview of genetics and genomics. Genetics is the study of individual genes or parts of genes, while genomics is more holistic, involving the study of all the genes of an organism (the genome) and their interrelationships to identify their combined influence on growth and development.

There are three components of genomics: DNA sequencing, bioinformatics and recombinant DNA. Genetics involves a huge amount of data, so the development of inexpensive computing power has been fundamental.

The tools used in genetics include:
• DNA sequencing
• Bioinformatics
• Markers
• Genome mapping
• Gene identification
• Gene expression
• Recombinant DNA
• Marker-assisted selection

Meredith added that while methods have become more refined over time, genetic modification is as old as agriculture. Farmers have selected clones using the variation that is naturally present in plant varieties, and they’ve also crossed another grape variety or grape species with different traits.

Molecular genetic modification (“genetic engineering”), however, is new. It adds characteristics from another variety, grape species, plant, animal, insect or microbe using directed and specific changes that add, modify or eliminate a single gene or several genes.

Its goal is the transfer of a trait from one species to another.

In traditional genetics you cross plants, then use repeated backcrosses to achieve the goal. This can take a long time to modify, evaluate and grow grapevines, then evaluate wines made from them using conventional techniques.

Genetic engineering allows scientists to transfer a single trait by isolating a gene and introducing it into a vine.

The biggest difference between the two techniques is that with traditional genetics, the plants must be crossable (that is, they must both be grapevines). With genetic engineering, the source of the genes can be any organism.

Both methods require extensive evaluation for several years in multiple sites, greenhouse testing, field evaluation, expression of the added trait (like resistance to the disease or pest), retention of quality and performance such as flavor, yield and vigor. This takes many years.

Looming over all genetic modification is some economic reality: Consumers are used to identifying wines by variety in the United States. If you modify a vine, can you still call it Cabernet Sauvignon? The rise of proprietary wine blends could reduce this problem, but most wines are still sold by variety. It’s not clear if consumer will accept new grape varieties.

There are also issues of intellectual property rights and patents.

Moreover, there are widespread concerns among people about the safety of genetically engineered plants and concern that they could damage the environment—issues scientists must address if improved grapevines are to be accepted.

Breeding PD-resistant wine grapes
Against this background, Andy Walker discussed his work breeding PD-resistant wine grapes using traditional crossing and selection aided by advance tools.

One of his lab’s focuses is on developing grapevines resistant to Pierce’s disease. Some grapevines with resistance already exist. One of them is Lenoir (also called Jacquez or Black Spanish), an apparently naturally occurring hybrid of Vitis aestivalis and Vitis vinifera, but it doesn’t make very good wine. It’s used primarily for Port-like sweet wines in Texas.

More recently, researchers at the University of Florida developed Blanc du Bois, the culmination of hundreds of years of breeding native Florida grapes resistant to PD with vinifera grapes. It makes decent white wine, but its development involved multiples genes.

More recently, Walker’s team discovered a strain of Vitis arizonica (b43-17) from north Mexico, where a single dominant gene provides the resistance. They genetically and physically mapped the gene.

Using marker-assisted selection that allows them to speed up the development and evaluation for vines with specific traits, they were able to get flowers and fruit in the second year from DNA extracted from seedlings.

They selected for lack of symptoms of PD and low bacterial levels with repeated back crosses to produce vines that were 50% vinifera, then 75%, 88%, 94% and 97%—as far as Walker feels they need to go. Walker’s team didn’t stop the process to make and test wines at early levels, but they have made it from later crosses.

Walker has grown various versions of these vines in Davis and Napa Valley, Calif., Fredericksburg, Texas, Auburn, Ala., and Gainesville, Fla., and has new plantings in Temecula, Calif., as well as some other sites.

This process simply optimizes classical breeding; it doesn’t involve genetically modified organisms.

Among the most promising vines are four 94% vinifera reds and three 94% whites as well as eight 97% vinifera reds.

The blends use different vinifera varieties for the same reason cousins shouldn’t breed: potential for concentrating faults; but red genes from varieties can be used to produce white wine and vice versa.

Many of the grapes have been made into wine, and Walker provided samples of some 94% vinifera wine to the audience. They showed no undesirable flavors or aromas and suggested wines from various locations—though not necessarily Cabernet or Chardonnay, for example.

Walker’s research team also developed three PD-resistant rootstocks. They continue the work producing other crosses, including some with resistance to PD from other sources.

Walker also mentioned powdery mildew resistance breeding being performed by various researchers. This is complicated, as there are different strains of powdery mildew, necessitating multiple sources of resistance.

His research has found resistance in various grape varieties including vinifera in the Middle East and Central Asia, the likely home of vinifera.

Resistance breeding for fanleaf virus
Finally, Marc Fuchs discussed work in breeding vines resistant to grapevine fanleaf virus (GFLV). He wanted to investigate whether a genetically modified organism would be a potential solution for GFLV, since other options haven’t been adequate.

Other options for managing the virus include planting clean vines, careful selection of the budwood and planting material, certification and clean stock, rogueing (removing infected plants) or allowing the vineyard to lie fallow—though that’s not a practical option for most property owners.

Other options include controlling nematodes with soil fumigation, using plants like marigold and hairy vetch with nematicidal properties or adopting tolerant rootstocks like 039-16, Freedom, RS-3 and GRN.

Unfortunately, there are no known sources of resistance in cultivated or wild grapevines, though one possibility is inoculating vines against the virus with a mild form of the disease just as we vaccinate people against diseases. This has shown some promise.

Finally, another possible solution would be a pathogen-derived resistance using interference to the virus’ RNA via a genetically modified organism.

Fuchs noted that genetically engineered papayas are now on the market to overcome papaya ringspot virus, which threatened to wipe out cultivation in Hawaii.

Genetically modified rootstock might be a potential solution for grapevine fanleaf virus infection, but it’s a challenging effort as there are many forms of the virus, and the rootstock would have to be resistant to all of them. Fuchs added that scientists haven’t developed such a rootstock, and he’s not even sure it would help. “It won’t be the ultimate solution. Perhaps we could combine it with Andy (Walker)’s work with traditional breeding using advance processes.”

Posted on 04.16.2016 - 19:14:24 PST
Wonderful article and the insights included here are great for us reading on the east coast.

There's hardly any pushback here about grape growers and winemakers using hybrid varieties in their wings stemming from a GMO-fear. There could be any number of reasons why we could conclude that's the case but still fascinating to consider!